title: Tyrosinase inhibitory constituents from the bark of Peltophorum dasyrachis (yellow batai).
abstract: Tyrosinase inhibitory activity-guided fractionation of the bark of Peltophorum dasyrachis (yellow batai) led to the isolation of the six active compounds which were characterised as six flavonoids: apigenin (1), (+)-2,3-trans-dihydrokaempferol (2), (+)-2,3-trans-dihydrokaempferol-3-O-α-L-rhamnoside (3), (+)-4',7-dimethoxy-2,3-trans-dihydroquercetin (4), (+)-2,3-trans-dihydroquercetin (5) and (-)-2,3-trans-dihydroquercetin-3-O-α-L-rhamnoside (6). All compounds were isolated for the first time from the bark of P. dasyrachis. Moreover, all compounds were evaluated for tyrosinase activities towards L-DOPA as the substrate. We observed that compounds 2 and 5 showed potent inhibitory effects (IC₅₀ values were 126 ± 3.2 and 210 ± 5.8 µM, respectively). In general, for flavonoids the 3',4'-dihydroxy group's substituent is a more potent inhibitor than the 4'-hydroxy group substituent, i.e. quercetin > kaempferol. Interestingly, our result in the oxidation of L-DOPA showed that the 4'-hydroxy group substituent (compound 2) is a more potent inhibitor than the 3',4'-dihydroxy group substituent (compound 5). This result showed a new relationship between tyrosinase inhibitory activities and flavonoids. The kinetic analyses by Lineweaver-Burk plots showed that both the compounds 2 and 5 behaved as competitive inhibitors of L-DOPA oxidation.
authors.affiliation: Department of Applied Chemistry, Faculty of Science of Engineering, Kinki University, 3-4-1 Kowakae, Higashiosaka-shi, Osaka 577-8502, Japan.
authors.forename: Mai
authors.initials: M
authors.lastname: Fujiwara
authors.forename: Nobuo
authors.initials: N
authors.lastname: Yagi
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Miyazawa
mesh_terms: D047310:Apigenin / Q000302:isolation & purification / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000302:isolation & purification / Q000494:pharmacology; D007887:Fabaceae / Q000737:chemistry*; D020128:Inhibitory Concentration 50; D044949:Kaempferols / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors*; D024301:Plant Bark / Q000737:chemistry; D010936:Plant Extracts / Q000302:isolation & purification / Q000494:pharmacology; D011794:Quercetin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D044949:Kaempferols; D010936:Plant Extracts; D047310:Apigenin; D011794:Quercetin; D014442:Monophenol Monooxygenase